Automotive air conditioning compressors of either the piston or scroll type generally use reed-type, one-way refrigerant flow control valves, especially as discharge valves. A flat valve plate separates a gas compression chamber from a discharge chamber, with one or more round refrigerant discharge ports opening between the two. An elongated flat, spring steel reed has a base fixed to the valve plate and a tip overlaying the discharge port. Positive pressure forces the reed tip up and away from the valve plate surface to admit pressurized refrigerant vapor through the port and into the discharge chamber, but reverse flow is prevented as the reed snaps quickly back down over the port. A rigid, upwardly bent stop resting over the reed limits its opening height. The undersurface of the reed tip must make complete contact with the valve plate surface, all around the discharge port edge, in order to provide a good back flow preventing seal. However, it has been found that if the entire undersurface of the reed tip contacts the surface of the valve plate, it can tend to stick to the surface and not open quickly enough. Furthermore, the slapping noise of closing contact may be excessive. Therefore, it has been common practice for years to recess an annular channel concentrically around the port, greater in diameter than the reed tip, leaving a relatively narrow reed tip support seat surrounding the port.
Referring first to FIGS. 1 through 3, a typical example of the type of prior art discharge reed valve referred to above is illustrated. A compressor housing 10 has a compression space 12 segregated from a discharge chamber 14 by a flat discharge plate 16. A round, sharp-edged discharge port 18 opens through plate 16, with an exemplary diameter of 8.5 mm. One-way only refrigerant vapor flow through port 18 is assured by a conventional, flexible reed, indicated generally at 20. Reed 20 is a thin (0.4 mm), resilient spring steel member which is symmetric to a dotted line length axis A with an effective length of approximately 15.5 mm. A base 22 is riveted to plate 16, and a generally circular tip 24 concentrically overlies the discharge port 18, with a diameter of approximately 11.5 mm. Tip 24 could be straight on the sides, and rounded only at the distal edge, and is in some designs, but works in the same way. A rigid stop 26 of corresponding size overlies reed 20, so that the tip 24 is limited in how far away from the port 18 it can flex when lifting in response to a positive pressure between chamber 12 and 14. A negative pressure differential, in conjunction with the reed 20's own tendency to return to its flat condition, causes it to slap down against the surface of plate 16 to close port 18, passively creating a one-way only flow through port 18. In order to reduce the noise of the reed tip 24, slapping down shut, as well as to reduce the "stiction" resistance to its opening, the surface of plate 16 located below the reed tip 24 and surrounding port 18 is largely recessed by a concentric annular channel 28 having an outer diameter of approximately 13.6 mm, greater than the reed tip diameter 24 of 11.5 mm, and an inner diameter of approximately 10.1 mm, less than the reed tip 24 and approximately 1.6 mm greater than the discharge port 16. Formation of the channel 28 leaves a narrow, annular support seat 30 completely and concentrically surrounding port 16, with a constant radial width W1 of approximately half the diameter difference, or 0.8 mm all the way around. The channel 28 assures that most of the undersurface of reed tip 24 makes no surface contact as it slaps shut, reducing engagement noise. Conversely, the circumferentially complete surface of seat 30 assures complete sealing around port 16, but provides a reduced contact surface area to stick to the undersurface of tip 24 and retard its lifting and opening. The surface area of seat 30 must still be large enough to support the tip 24 against bending or "cupping" as it slaps down, however. Otherwise, reed tip fracture could occur, especially near the distal edge, where the forces and speed of closing are greatest.
Other approaches to reducing sticking include shot peening or other surface treatments and roughening around the edge of the discharge port. However, these are more expensive and difficult to control than the simple expedient of forming an annular channel. While the resulting, constant width annular support seat created by the channel works, it would be desirable to further optimize it, if possible, to further reduce engagement noise and opening resistance, while still providing adequate reed tip support.